The present invention relates to an infusion device for medical use.
In particular, the device of the invention is used in apparatus for the extracorporeal treatment of blood, for example apparatus for dialysis and/or plasmapheresis, in order to provide an infusion line which can be connected to an extracorporeal blood circuit associated with the aforementioned apparatus; the device in question can also be used for forming an infusion line which can be connected directly to the patient's vascular system.
As is known, a conventional infusion line comprises at least one length of tubing designed to connect a bag containing a specified infusion liquid to an extracorporeal blood circuit or directly to a patient through conventional access means such as needles, catheters or the like.
A pump, of the peristaltic type for example, can be provided on the infusion line for moving the infusion fluid in the desired way. For example, U.S. Pat. No. 5,698,090 in the name of Hospal Industrie describes an infusion line comprising a bag containing a replacement liquid, associated for operation with a balance designed to measure the weight of the bag and send a corresponding electrical signal to a control unit.
The control unit also acts on a peristaltic pump positioned on the infusion line; in particular, the unit controls the angular velocity of the pump in a suitable way according to the difference between the actual consumption signalled by the balance and the value set by the user.
Downstream of the peristaltic pump, the infusion line is connected to a collection chamber in which the infusion liquid can be combined with the blood obtained from a venous branch of an extracorporeal blood circuit.
Downstream of the aforesaid chamber, the blood, having been enriched with the infusion liquid, is returned to the patient's cardiovascular system.
The device described above can be used to control the actual flow and consequently the velocity of the infusion pump, and to achieve a separation of liquid and air such that the propagation of dangerous gas particles towards the patient is prevented.
Because of the presence of the balance and the control unit, if the total contents of liquid in the bag are known, the pump can be stopped and the suction of air bubbles from the bag prevented when the condition is reached in which the liquid in the bag has been used up.
However, it should be noted that there is an intrinsic minimum time interval between the actual emptying of the bag and the detection of this situation by the system consisting of the balance combined with the control unit. Consequently, in order to ensure the reliable operation of the described system, it is necessary to have a collection chamber (often referred to as a “bubble trap”) in the infusion line, in which a specified volume of liquid can be held constantly; in normal operating conditions, the collection chamber holds this specified volume of fluid and enables the control system and balance to have sufficient time to detect when the end of infusion condition has actually been reached.
It should be noted that the detection of an end of infusion condition at the correct time is also important for the purpose of avoiding a discrepancy between the prescribed amount of infusion liquid for the patient and the actual infusion provided by the machine.
In addition to the solution described above, in which a balance is used to detect the end of infusion condition, widespread use has also been made in the past of solutions using level sensors, of the optical and/or ultrasonic type for example, which can interact with an infusion liquid collecting chamber, typically located in an intermediate area of the infusion line.
In the presence of a specified flow of liquid from the bag, the infusion liquid collecting chamber forms a liquid level and a reservoir for separating any air bubbles.
A level sensor associated with the chamber can be used to check and detect any fall in the level, permitting immediate recognition of a danger condition caused by the end of the supply of infusion liquid.
Clearly, if they are to operate correctly, the level sensors described above for detecting any fall in level or the presence of air bubbles in the flow directed towards the patient also require the presence of a collection chamber in the infusion line, for the formation of a level which will be detectable.
In other words, according to the known technical solutions, in order to enable an end of infusion condition to be detected and to ensure the reliable separation of air from the fluid directed towards the patient, it is necessary to provide a proper collection chamber or drip chamber in the infusion line, where the infusion fluid can accumulate, thus considerably reducing its velocity.
In practice, the collection chamber has a radial dimension considerably greater than that of the infusion tube, and, in the manufacturing process, is typically made separately from the rest of the line. The various lengths of tubing forming the infusion line and the collection chamber then undergo a rather complicated assembly process which considerably increases the total costs of the infusion line.
Furthermore, in the case of infusion lines interacting with level sensors, it is necessary to use optical or acoustic detectors which further increase the weight of the structure of the device. The control system has to be programmed to coordinate and control the signals received from the sensors.
Finally, all the known devices require the presence, downstream of the pump, of at least one safety valve, for example a clamp, which can close the tubing as soon as the condition of the end of infusion or the approaching end of infusion is detected.
Clearly, the fluid collection chamber can separate air from the liquid only when a minimum quantity of liquid is present in the chamber: if the liquid in the collection chamber is used up (this inevitably occurs after a certain time when the infusion liquid has been used up, unless the infusion pump is stopped at the correct time), there will be a transfer of gas towards the patient.
Finally, it should also be mentioned that there are known air-liquid separators of the type comprising a containing body forming two adjacent chambers separated by a hydrophilic membrane; the containing body has an inlet aperture for a fluid comprising liquid and gas particles. The liquid can pass through the hydrophilic membrane and emerge through an outlet aperture. The gas which reaches the first chamber is discharged through secondary apertures positioned upstream of the hydrophilic membrane, at least one hydrophobic membrane being used at these apertures to prevent the liquid from passing through.
The device which has been described allows the fluid, containing gas particles, to be separated into two parts, namely a liquid portion which emerges from the outlet aperture provided in the second chamber, and a gas portion which is released through the secondary apertures provided in the first chamber.
It should be noted that the air separator device which has been described does not require a constant presence of liquid stagnating within it in order to separate the gas; in other words, the fluid passing through the separation device is continuously divided into liquid, which continues along the line, and gas, which is discharged to the exterior.